The corn kernel, illustrated in FIG. 1, has a number of components, each being best suited for various uses. The process of modern dry corn milling seeks to segregate and separately process the below-identified parts of a kernel of corn as each part has a separate use. The hard outer shell is called the pericarp or the bran coat. The end of the corn kernel which adheres it to the corn cob is called the tip cap. The interior of the corn kernel consists of the endosperm and the germ. The endosperm is generally broken into two parts: soft endosperm and hard endosperm. For purposes of human consumption, the hard endosperm generally produces grits and corn meal, and the soft endosperm generally produces corn flour. The germ contains a much higher percentage of fat compared to the other parts of the kernel and is the source of corn oil.
Corn milling is an ancient practice to the human race, dating back many, many years. Historically, mill stones were utilized to grind the corn into meal. Wind and water powered mills developed several hundred years ago allowed for increased efficiency in the processing of corn. For the last hundred years or so, milling operations have utilized roll milling equipment in an effort to separate the components of the corn kernel for more particularized uses.
Modern roll milling equipment utilizes contiguous rollers with varying sized corrugations and varying sized roller gap spacings to achieve the desired particle size fractionation. Typically, mills employ rollers in series with increasingly narrow gaps in a gradual milling process. More specifically, the various parts of the corn kernel are segregated and removed to differing processing pathways, often referred to as streams. Initially, after cleaning the hard outer shell, the kernel is fractured via a mechanical process thereby freeing and removing the germ from the remaining parts of the kernel—a step called degermination. The remaining parts of the kernel are broken up by a series of rollers. As this material is processed, the hard outer shell is removed in the form of bran flakes, and the remaining soft and hard endosperm are further separated into differing streams by passing through a series of rollers and sifters which separate product by particle size. The end products of the dry corn milling operation are bran, grits, meal, flour, and high fat germ.
A flow scheme typical of prior art mills is illustrated in U.S. Pat. No. 5,250,313. In FIG. 5 of the '313 patent (reproduced herein as FIG. 2), the incoming corn is cleaned, washed, tempered to the appropriate moisture content, fractured or degerminated, and dried. Various designs exist to carry out the step of degermination. For example, the Ocrim degerminator uses a spinning rotor having combination blades to operate against a horizontal, perforated cylinder that only allows partial kernels to pass. The rotor and breaker bars are set to break the corn against a spiral rotor bar and a cutting bar. Another known degerminator is the Beall degerminator. In the Beall degerminator, grinding occurs through an abrasive action of kernel against kernel, and kernel against a nested conical surface and screen. Impact-type degerminators are also used. An example is the Entoletor degerminator as illustrated in FIG. 3. The Entoletor includes a vertical drive shaft that operates a rotor. Kernels are fed downwardly towards the rotor where they are forced outwardly by centrifugal motion to impact a liner surface.
Generally, the product out of the degerminator is separated into a first stream which is relatively rich in endosperm and a second stream which is relatively rich in germ and bran. Specifically, with reference again to FIG. 2, the degerminated corn is aspirated to effect initial density separation of the fractured kernel. The tailings and liftings from the aspirators are further separated through additional aspiration or the use of gravity tables. In general, bran, whole germ and germ contaminated particles obtained via density separation are lighter than other constituent parts and may be partially removed via gravity separation to be directed through a series of germ rollers and sifters. Separated, primarily endosperm-containing streams from the gravity tables and aspirators may be directed to different break rollers depending on the particle size of the stream. For example, those primarily endosperm-containing streams having smaller particle sizes may be directed past the first and second break rollers, or as illustrated in FIG. 2, beyond to later break rollers.
The “break rollers” used in a gradual break process typically comprise corrugated rollers having roller gaps that cascade from wider roller gaps for the 1st break roller to more narrow roller gaps for subsequent break rollers. Roller gaps are the spacings between the exterior or “tip” portions of the corrugations on opposing rollers. The use of 5 break rollers is typical, and roller gaps may vary depending on the desired finished product. Typical roller gap distances on prior art systems range from about 0.01 to about 0.07 inches, wherein smaller gaps result in finer particles. In general, the break rollers are operated such that opposing corrugated roller faces rotate at differing rates. FIG. 4 contains examples of typical prior art roller corrugation configurations. Most configurations present a sharp edge and a dull edge as determined by the slope of the corrugation surface. Therefore, breaking may occur under a sharp to sharp, sharp to dull, dull to sharp, or dull to dull arrangement of opposing corrugations.
After break rolling, the further-broken particles are separated, typically by a sifting process. From there, larger particles are further rolled in a subsequent break roller (and the further-broken particles are again sifted), or they are passed on to drying or cooling steps or additional sifting steps to isolate finished products (flour, meal, grits, etc.). Typical finished-product requirements may be found generally in 21 CFR §§ 137.215-285 (1993). Of course other products may be desired by particular purchasers. The remaining particles that fail to pass the post germ sifting steps are typically sent to a germ handling process (labeled oil recovery in FIG. 2). The finer particles obtained from the germ roller siftings are processed in a manner generally similar to the finer particles from the break rollers.
Traditionally, large scale corn mills have employed a great degree of redundancy and repetitive processing of the grain. For example, as illustrated in FIG. 2, a traditional corn milling process involves an initial degermination step, followed by five separate roller, or breaking, steps each of which is followed by sifting steps. In addition, the prior art includes various shorter mill processes wherein fewer roller steps are utilized, germ streams are extracted from the mill stream earlier in the process, and valuable capital, space and time savings are achieved. See for example the process described in the '313 patent. The shortened mill regimes also dramatically reduce production expense by lowering the labor costs associated with the milling process due to the reduced maintenance and monitoring required of a much shorter process.
Nevertheless, even in the prior art “shortened” mill flow regimes, inefficiencies remain. For example, U.S. Pat. No. 4,189,503 (a parent from which the '313 patent is a continuation-in-part), teaches the use of a preferred degermination and rolling process to avoid breakage of the germ. These patents also teach the separation of degermination products into three streams, one of which is a “fine” stream relative to the others (see FIGS. 6, 7, and 8 of the '313 patent and accompanying text). The '313 and '503 patents specifically teach the reintroduction of this fine stream into the other less carefully graded streams after the other streams have been subjected to various other steps, such as tempering and drying (See claim 8 of the '503 patent). The '313 and '503 patents therefore specifically teach the separation or gradation of post degermination product for the purpose of avoiding the addition of moisture to the separated fines (See '313 patent, Col. 11, Lines 4-14) followed by the subsequent reintroduction of the fine stream into a mixed stream. With only a reference to fines, these patents do not teach or provide motivation to isolate finished product streams as early in the milling process as a post degermination sifting. In fact, the '313 patent teaches a process wherein the product stream from the degerminator to the first break roll comprises bran, endosperm and germ. In addition, the reintroduction of the sifted “fines” streams into other streams “contaminates” the sifted stream and increase the flow across subsequent sifters.
FIG. 9 of the '313 patent does disclose a process wherein a combined stream having germ, grit, meal, and flour-sized particles, immediately downstream of a degerminator sifter, is passed to a secondary grading sifter and aspiration processes to separate flour, meal, brewer's grits, and a feed/oil recovery product without post-degermination rolling. It is shown, however, that the process of FIG. 9 in the '313 patent specifically depends upon the preferred degerminator described in the '313 patent and its parent applications. The '313 patent specifically distinguished its preferred degerminator over impact-type degerminators. The preferred degerminator of the '313 patent is described therein and claimed in the '503 patent, claim 1, et. seq.; U.S. Pat. No. 4,301,183, claim 1 et. seq.; and U.S. Pat. No. 4,365,546.